1. Field of the Invention
The present invention relates to an imaging lens used in an optical system of an image readout apparatus such as facsimile machine or image scanner and, in, particular, to a readout lens for reducing or enlarging images.
2. Description of the Prior Art
For an imaging lens used for reading out an image in a facsimile machine, an image scanner, or the like which is of a type forming an image of an original image onto an image pickup device such as CCD in a reduced or enlarged state, it has been basically required to have a high resolution at the imaging magnification used, a large peripheral light quantity, and a low distortion. Additionally, together with the recent demand for attaining a compact size and a low cost in the optical apparatus as a whole, it has been required to have a compact size and a low manufacturing cost.
As an imaging lens which can respond to such requirements, there has been known, for example, a compact imaging lens of four-sheet configuration disclosed in Japanese Unexamined Patent Publication No. 7-104185.
The four-sheet imaging lens disclosed in the above-mentioned publication can shorten the length of the whole lens system while attaining a favorable quality in the readout image. When used in a line sensor of a copying machine or the like, however, there has been an increasing demand for reading out images with a wider angle due to necessity for attaining a compact size or the like. Thus, readout lenses with a wider field have been required. Further, there has been a demand for attaining a readout lens brighter than that disclosed in the above-mentioned publication.